Universal primer

ABSTRACT

A radiation-curable composition comprising a radiation-curable compound, a free acid and a halogenated polyolefin is disclosed. The compositions are useful in the repair of damaged motor vehicle body parts.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a Continuation of U.S. patent applicationSer. No. 11/468,831 filed on Aug. 21, 2006, the entirety of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to primer compositions that are useful inthe refinishing of motor vehicles.

BACKGROUND OF THE INVENTION

In the refinishing of automobiles and trucks, a primer is usuallyapplied to the surface being repainted before application of a finishingor topcoat. The primer is formulated such that it promotes good adhesionto the substrate and to the topcoat. However, modern motor vehicles haveparts made of different materials. For example, areas such as the hoodand trunk decks that are not subject to a corrosive environment may bemade from cold rolled steel, whereas fenders and quarter panels whichare subject to road salt and other corrosive conditions are made fromgalvanized steel. Still other parts of the motor vehicle such as bumpersand fascia are made from plastic. It has been difficult to formulate aprimer composition that adheres well to all types of substrates.Further, it is important that a primer composition cure at lowtemperature since most refinish body shops do not have ovens to heat thecoating. Also, most plastic substrates cannot tolerate hightemperatures.

Therefore, it is desirable to have a universal primer composition thatcan be applied to substrates comprising mixed metals and plastic andwhich can be cured at low temperature providing good adhesion to suchsubstrates and to topcoats applied to the primer.

SUMMARY OF THE INVENTION

The present invention provides a radiation-curable compositioncomprising:

(a) a radiation-curable compound,

(b) a free acid, and

(c) a halogenated polyolefin.

The invention also provides a method of coating a substrate thatcomprises at least one metal and plastic comprising applying theradiation-curable composition to the substrate, exposing the coatedsubstrate to a source of ultraviolet radiation to cure the compositionand applying a topcoat to the cured composition.

DETAILED DESCRIPTION

Examples of suitable radiation-curable compounds include polyacrylatessuch as diacrylates and triacrylates. Specific examples includehexanediol diacrylate or tripropyleneglycol diacrylate, triacrylatessuch as trimethylolpropane triacrylate, alkoxylated trimethylolpropanetriacrylate or pentaerythritol triacrylate, polyacrylates such aspentaerythritol tetraacrylate or dipentaerythritol hexaacrylate, epoxyacrylates obtained for example by reacting epoxides with acrylic acidsuch as UVE 100 and UVE 150 available from Croda or Actilane 320 orActilane 330 available from Akcros Chemicals, or unsaturated polyesterssuch as polyesters prepared with maleic anhydride as one of themonomeric components. Preferably the primer contains 50-80% by weight,more preferably 60 to 70% by weight based on resin solids of the curablecomposition.

The composition of the invention is particularly useful as a primer formotor vehicles. The radiation-curable compound is meant to includemixtures of radiation polymerizable compounds including those mentionedabove and preferably a radiation polymerizable compound that contains aurethane moiety and is preferably a urethane polyacrylate. Morepreferably, the radiation-curable compound contains a urethanediacrylate. The urethane polyacrylates are typically prepared byreacting an isocyanate-functional compound with a hydroxyl-functionalacrylate. The urethane polyacrylate typically is present in amounts of50 to 100, preferably 60 to 80 percent by weight based on total weightof the radiation polymerizable compound.

The polyisocyanate that is reacted with the hydroxy functional acrylatecan be any organic polyisocyanate. The polyisocyanate may be aromatic,aliphatic, cycloaliphatic, or heterocyclic and may be unsubstituted orsubstituted. Many such organic polyisocyanates are known, examples ofwhich include: toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, andmixtures thereof; diphenylmethane-4,4′-diisocyanate,diphenylmethane-2,4′-diisocyanate and mixtures thereof; o-, m- and/orp-phenylene diisocyanate; biphenyl diisocyanate;3,3′-dimethyl-4,4′-diphenylene diisocyanate; propane-1,2-diisocyanateand propane-1,3-diisocyanate; butane-1,4-diisocyanate;hexane-1,6-diisocyanate; 2,2,4-trimethylhexane-1,6-diisocyanate; lysinemethyl ester diisocyanate; bis(isocyanatoethyl) fumarate; isophoronediisocyanate; ethylene diisocyanate; dodecane-1,12-diisocyanate;cyclobutane-1,3-diisocyanate; cyclo hexane-1,2-diisocyanate,cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate and mixturesthereof; methylcyclohexyl diisocyanate;hexahydrotoluene-2,4-diisocyanate; hexahydrotoluene-2,6-diisocyanate andmixtures thereof; hexahydrophenylene-1,3-diisocyanate;hexahydrophenylene-1,4-diisocyanate and mixtures thereof;perhydrodiphenylmethane-2,4′-diisocyanate,perhydrodiphenylmethane-4,4′-diisocyanate and mixtures thereof;4,4′-methylene bis(isocyanato cyclohexane) available from Mobay ChemicalCompany as Desmodur W; 3,3′-dichloro-4,4′-diisocyanatobiphenyl,tris(4-isocyanatophenyl)methane; 1,5-diisocyanatonaphthalene,hydrogenated toluene diisocyanate;1-isocyanatomethyl-5-isocyanato-1,3,3-trimethylcyclohexane and1,3,5-tris(6-isocyanatohexyl)-biuret.

Examples of hydroxyl-functional acrylates which can be reacted with thepolyisocyanate polyurethanes to form the urethane acrylates include:2-hydroxyethyl (meth)acrylate; glycerol di(meth)acrylate; the(meth)acrylates of the glycidyl ethers of butanol, bisphenol-A,butanediol, diethylene glycol, trimethylolpropane and other mono-, di-,tri- and polyhydric alcohols; the (meth)acrylates of epoxides such asstyrene oxide, 1-hexane oxide, 1-decene oxide, 1-butene oxide; the(meth)acrylates of epoxidized fatty acids such as linoleic and linolenicacid; the (meth)acrylates of epoxidized linseed and soya oils; 2- and3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate; andhalogenated hydroxyalkyl acrylates such as 3-chloro-2-hydroxypropyl(meth)acrylate; 3-bromo-2-hydroxypropyl (meth)acrylate;2-chloro-1-(hydroxymethyl)ethyl (meth)acrylate, and2-bromo-1-(hydroxymethyl)ethyl (meth)acrylate. Wherever used in thespecification and claims herein, it is to be understood that the term“acrylate” is intended to include “methacrylate” and may be expressed as(meth)acrylate.

Other useful hydroxyl-functional compounds having ethylenic unsaturationthat can be reacted with the polyisocyanate include allyl alcohol andderivatives thereof.

It should be understood that the hydroxyl-functional acrylates and thepolyisocyanates can be prereacted to form an isocyanate-functionalacrylate that is then reacted with a polyol to form the polyurethanepolyacrylate. Similarly, isocyanate-functional acrylates such asisocyanato ethyl acrylate can be reacted with a polyol to form thepolyurethane polyacrylate. Further, other ethylenically unsaturatedisocyanate-functional compounds such as vinyl isocyanate andallylisocyanate can be reacted with a polyol to form an ethylenicallyunsaturated polyurethane.

Examples of polyols are simple diols, triols, and higher hydricalcohols. Specific examples include 1,3-propanediol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 2,3-butanediol,2,2,4-trimethyl-1,3-pentanediol, 1,5-pentanediol, 2,4-pentanediol,1,6-hexanediol, 2,5-hexanediol, 1,7-heptanediol, 2,4-heptanediol,1,8-octanediol, 1,9-nonanediol, 4,5-nonanediol, 1,10-decanediol,1,9-decanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol,2-ethyl-1,3-hexanediol, 2,2-dimethyl-1,3-propanediol,2-ethylbutane-1,4-diol, 2,2-diethylpropane-1,3-diol,2,2-dimethylpropane-1,3-diol, 3-methyl-pentane-1,4-diol,2,2-diethylbutane-1,3-diol, 1,1,1-trimethylolpropane, trimethylolethane,1,4-cyclohexanediol, 1,4-cyclohexanedimethanol,1,2-bis(hydroxymethyl)cyclohexane, 1,2-bis(hydroxyethyl) cyclohexane,ethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol, dipropylene glycol, neopentyl glycol, glycerol, pentaerythritol,erythritol, sorbitol, mannitol, and the like. Ethylenically unsaturatedpolyhydric alcohols such as 2-butene-1,4-diol may be used alone or inadmixture with the saturated polyhydric alcohols. Of course, mixtures ofsaturated polyhydric alcohols or mixtures of unsaturated polyhydricalcohols may be employed.

The radiation polymerizable may contain a polythiol compound thatimproves the surface hardness of the cured coating. Examples includepentaerythritol tetrakis mercaptopropionate, trimethylolpropane tristhioglycolate. Also polymeric polythiols can be used. Examples arehydroxyl functional oligomer or polymer such as polyester polyols andhydroxyl-functional acrylic copolymers reacted with mercaptopropionicacid or thiol glycolic acid. When present, the polythiol compound ispresent in amounts of 2 to 30, preferably 5-25 percent by weight basedon total weight of the radiation polymerizable compound

The radiation-curable composition typically contains a photoinitiatorthat consists of any photoinitiators that are capable of generating freeradicals when exposed to UV radiation. A preferred class ofphotoinitiator is bis acyl phosphine oxides, for example Irgacure 819available from Ciba.

Preferably the radiation-curable composition contains 1-3% by weight ofphotoinitiator based on weight of resin solids of the radiation-curablecomposition.

The radiation-curable composition contains a free acid that promotesadhesion to metals. The term “free acid” is meant to encompass organicand/or inorganic acids that are included as a separate component of thecompositions of the present invention as opposed to any acids that areused in forming any of the components present in the radiation-curablecompositions or are present as an impurity with such components or aresomehow released when such components react. In certain embodiments, thefree acid included within the coating compositions of the presentinvention is selected from tannic acid, gallic acid, phosphoric acid,phosphorous acid, citric acid, malonic acid, or derivatives thereof, ormixtures thereof. Suitable derivatives include esters, amides, and/ormetal complexes of such acids.

In certain embodiments, the free acid comprises an organic acid, such astannic acid, i.e., tannin. Tannins are extracted from various plants andtrees that can be classified according to their chemical properties as(a) hydrolyzable tannins, (b) condensed tannins, and (c) mixed tanninscontaining both hydrolyzable and condensed tannins. Tannins useful inthe present invention include those that contain a tannin extract fromnaturally occurring plants and trees, and are normally referred to asvegetable tannins. Suitable vegetable tannins include the crude,ordinary or hot-water-soluble condensed vegetable tannins, such asQuebracho, mimosa, mangrove, spruce, hemlock, gabien, wattles, catechu,uranday, tea, larch, myrobalan, chestnut wood, divi-divi, valonia,summac, chinchona, oak, etc. These vegetable tannins are not purechemical compounds with known structures, but rather contain numerouscomponents including phenolic moieties such as catechol, pyrogallol,etc., condensed into a complicated polymeric structure.

In certain embodiments, the free acid comprises a phosphoric acid, suchas a 100 percent orthophosphoric acid, superphosphoric acid or theaqueous solutions thereof, such as a 70 to 90 percent phosphoric acidsolution.

The free acid is present in the radiation-curable composition in anamount ranging from 0.1 to 5.0 weight percent, such as 0.5 to 1.5 weightpercent, based on total weight of resin solids present in thecomposition.

To promote adhesion to plastics, the radiation-curable compositioncontains a halogenated polyolefin, that is, polyolefins that include oneor more other halogen atoms, such as fluorine, chlorine, bromine, oriodine. Chlorinated polyolefins or CPOs are preferred.

CPOs suitable for use in the composition applied by the firstapplication technique in certain methods of the present invention may,in certain embodiments, have a weight average molecular weight rangingfrom about 10,000 to about 150,000, such as about 20,000 to about125,000, such as about 25,000 to about 105,000, as determined by gelpermeation chromatography using a polystyrene standard. Examples ofsuitable CPOs are disclosed in U.S. Pat. Nos. 6,593,423; 4,997,882;5,319,032; and 5,397,602, herein incorporated by reference. SuitableCPOs for use in the methods and systems of the present invention includematerials commercially available from Eastman Chemical Products, Inc.,of Rochester, N.Y. For example, CPOs available from Eastman Chemicalsunder the names CP153-2, CP164-1, CP343-1, CP343-3 and CP515-2 may beused. In addition, the Hardlen® CPO adhesion promoters available fromToyo Kasai Kogyo Co., Ltd., of Osaka, Japan may be used.

Preferably, the halogenated polyolefin is modified by grafting acompatibilizing material such as an acrylic monomer onto the polyolefin.As used herein, the term “compatibilizing material” refers to moietiesthat modify a halogenated polyolefin so as to render the halogenatedpolyolefin compatible with the radiation-curable compound. By“compatible” it is meant herein that the halogenated polyolefin and theradiation-curable compound do not separate from each other in thecomposition.

Particular examples of acrylic monomers that may be grafted onto ahalogenated polyolefin to produce a modified halogenated polyolefinsuitable for use in the present invention include, without limitation,acrylic acid, methacrylic acid, and esters thereof, such as acrylatesand methacrylates. Useful esters of acrylic or methacrylic acid includestraight chain or branched alkyl or hydroxyalkyl esters of acrylic ormethacrylic acid. Useful alkyl esters can contain about 1 to about 24carbon atoms, and preferably contain about 1 to about 18 carbon atoms.Non-limiting examples of alkyl esters include methyl (meth)acrylate,ethyl (meth)acrylates, propyl (meth)acrylates, butyl (meth)acrylates,pentyl (meth)acrylates, hexyl (meth)acrylates, heptyl (meth)acrylates,octyl (meth)acrylates, nonyl (meth)acrylates, decyl (meth)acrylates,dodecyl (meth)acrylates, tetradecyl (meth)acrylates, hexadecyl(meth)acrylates, ethylhexyl (meth)acrylates, lauryl (meth)acrylates,stearyl (meth)acrylates and 2-ethylhexyl (meth)acrylate. Suitablehydroxyalkyl esters include 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate andhydroxybutyl (meth)acrylate. As used herein, “(meth)acrylate” and termsderived therefrom are intended to include both acrylate andmethacrylate.

In certain embodiments, modified halogenated polyolefins suitable foruse in the methods and systems of the present invention may be producedby an atom transfer radical polymerization process (ATRP), such as isdescribed in U.S. Pat. No. 6,576,722 at col. 3, line 61, to col. 10,line 17, which is incorporated herein by reference.

In certain embodiments, modified halogenated polyolefins suitable foruse in the methods and systems of the present invention may be producedby conventional free radical polymerization methods that will beunderstood by those skilled in the art. See Kirk-Othmer Encyclopedia ofChemical Technology, Vol. 1 (1963). As will be understood by the skilledartisan, such radical polymerization is typically conducted in asolution of organic solvent(s). For example, aromatic solvents, such astoluene, xylene and SOLVESSO 100 may be used. Moreover, conventionalradical reaction initiators may be used, such as peroxides, includingbenzoyl peroxide, lauroyl peroxide, t-butyl hydroperoxide, andt-butylperoxy-2-ethylhexanoate; and azo compounds, includingazobisvaleronitrile, azobisisobutylronitrile andazobis(2-methylpropionitrile).

It will be appreciated by the skilled artisan that the compoundsproduced by a conventional free radical polymerization process willtypically comprise a mixture of polymers. For example, when grafting anacrylic monomer onto a CPO by conventional free radical polymerization,the random nature of standard radical polymerization will likely producea resin composition comprising a mixture of non-graft CPO chains,acrylic polymers, and CPOs having an acrylic monomer grafted thereon.Nevertheless, such a polymerization will produce at least some of themodified halogenated polyolefins that may be used in the methods andsystems of the present invention. Thus, in certain embodiments, theadhesion-promoting agent comprises a mixture of a halogenatedpolyolefin, an acrylic polymer, and a modified halogenated polyolefin.In these embodiments, the modified halogenated polyolefin may, forexample, comprise 1 to 75 percent by weight based on the total weight ofthe mixture of polymers. In such embodiments, the amount of modifiedhalogenated polyolefin that may be present in the mixture can rangebetween any combination of the recited values, inclusive of the recitedvalues.

The halogenated polyolefin including the modified material generallycomprises 1 to 10 percent by weight or, in some embodiments, 1 to 5percent by weight, or, in yet other embodiments, 1 to 2 percent byweight of the radiation-curable composition based on weight of totalresin solids present in the composition.

The radiation-curable composition may also comprise an organic solvent.Suitable organic solvents include, without limitation, xylene, toluene,Aromatic 100 solvent, which is commercially available from CumberlandProducts, Inc., Hodgenville, Ky., and alcohols, such as ethyl alcohol,propyl alcohol and diacetone alcohol, including mixtures thereof.

The organic solvent typically comprises 0 to 75, preferably 0 to 50percent by weight based on total weight of the radiation-curablecomposition.

The radiation-curable composition usually contains a pigment or filler.In principle any known pigment or filler can be used. Conventionalpigments such as titanium dioxide and zinc oxide can be included.Suitable fillers include clays, barytes, mica, talcs and calciumcarbonate. The compositions can include those pigments that are known toinhibit corrosion such as strontium chromate, zinc phosphate and bariummetaborate.

Preferred pigments and fillers are those that do not interferesubstantially with the radical cure. Preferably the pigment consistsprincipally of zinc sulphide, barium sulphate, china clay and corrosioninhibiting pigments. More preferably the pigment consists principally ofchina clay and corrosion inhibiting pigments. China clay is hydratedaluminium silicate obtained from sedimentary kaolin clays. An example ofa suitable china clay is Speswhite china clay available from ECCInternational.

The types and levels of pigments are chosen principally in order toachieve good sandability and corrosion resistance. Preferably the levelsand types of pigments and fillers are chosen to achieve a pigment volumeconcentration (PVC) of 10-50%, more preferably 15-25%. The PVC is theratio of the volume of pigment to the total volume of non-volatilematerial present in the whole composition expressed as a percentage.

The radiation-curable composition may also contain conventionaladditives such as adhesion promoters, pigment dispersants, flow aids,wetting aids and rheology modifiers. When present, these ingredientsconstitute no more than 20% by weight of the composition based on totalweight of the composition.

The radiation-curable compositions can be applied over a wide variety ofmetals and plastics. Examples of suitable metallic substrates caninclude ferrous metals and non-ferrous metals. Suitable ferrous metalsinclude iron, steel, and alloys thereof. Non-limiting examples of usefulsteel materials include cold-rolled steel, galvanized (zinc coated)steel, electrogalvanized steel, stainless steel, pickled steel,GALVANNEAL®, GALVALUME®, and GALVAN® zinc-aluminum alloys coated uponsteel, and combinations thereof. Useful non-ferrous metals includealuminum, zinc, magnesium and alloys thereof. Combinations or compositesof ferrous and non-ferrous metals can also be present.

Examples of plastic substrates are EVA (ethyl vinyl acetate) foam;polyurethane; fiberglass reinforced plastic; plastic includingthermoplastic and/or thermoset materials as known to those in the art,and as described below. Polyurethane substrates include aromatic,aliphatic and hybrid (hybrid examples are silicone polyether orpolyester urethane and silicone carbonate urethane). The polyurethanemay be thermosetting such as associated with reaction injection moldingmaterials (RIM) or may be thermoplastic such as polyester or polyetherbased thermoplastic urethanes. By “plastic” is meant the EVA andpolyurethanes mentioned above and any of the common thermoplastic orthermosetting synthetic materials, including thermoplastic olefins(“TPO”) such as polyethylene and polypropylene and blends thereof,thermoplastic urethane, polycarbonate, sheet molding compound,reaction-injection molding compound, acrylonitrile-based materials,nylon, and the like. A particular plastic is TPO that comprisespolypropylene and EPDM (ethylene propylene diene monomer).

The radiation-curable compositions of the present invention can beapplied to the substrates mentioned above by any of the conventionalcoating techniques such as, for example, brushing, spraying, dipping orflowing. Any of the known spray techniques can be employed such ascompressed air spraying, electrostatic spraying including either manualor automatic methods. In certain embodiments, the coating composition isapplied such that a dry film thickness in the range of 20 to 200 microns(0.8 mils to 8.0 mils) is obtained.

The primer composition is cured by exposure to UV radiation. Whenseveral applications are used, the primer can be cured after eachapplication or only after the final application. The ratio of UV-Bcontent to UV-A content of the radiation is preferably 1:1 or less. Morepreferably, the UV-B to UV-A ratio is 0.2:1 or less, most preferably0.05:1 or less and even more preferably 0.025:1 or less. The radiationpreferably has substantially no UV-C content. UV-A radiation is anyradiation falling within the 320-400 nm wavelength interval, UV-Bradiation is any radiation falling within the 280-320 nm wavelength andUV-C radiation is any radiation falling within the 100-280 nm wavelengthinterval.

The radiation may be provided by any suitable UV lamp and preferably thelamp(s) are positioned so that they are between 5 and 60 cm away fromthe surface of the primer. More preferably the lamp(s) are positioned sothat they are from 10 to 30 cm away from the surface of the primer.

Preferably the primer is exposed to the UV radiation for from 30 secondsto 10 minutes, more preferably from 1 to 3 minutes.

The primer can be sanded using sand- or glasspaper prior to topcoating.

The primer may be topcoated with any suitable refinish system in orderto achieve the desired final color and appearance. For example theprimer can be coated with a waterborne basecoat such as available fromPPG Industries under the trademark ENVIROBASE followed by a solventbornetwo-pack polyurethane clearcoat such as GLOBAL D893 available from PPGIndustries. Alternatively it can be topcoated with a solventbornebasecoat such as GLOBAL BC 9700 available from PPG Industries followedby a solventborne two-pack polyurethane clearcoat such as DELTRON DCU2042 available from PPG Industries. Alternatively it can be topcoatedwith a solventborne single layer two-pack polyurethane topcoat such asCONCEPT COLOR DCC 9300 available from PPG Industries.

The invention will now be illustrated by means of the followingexamples.

EXAMPLES

Illustrating the invention are the following examples that are not to beconsidered as limiting the invention to their details. All parts andpercentages in the examples, as well as throughout the specification,are by weight unless otherwise indicated.

A urethane polyacrylate suitable for use in the present invention wasprepared by equipping a 12-liter reactor vessel with a stirring blade,nitrogen inlet, and one feed inlet. Charge 1 (see below) was added tothe vessel.

CHARGE 1 Component Weight (g) T-1890¹ 4125.0 IONOL² 0.8 Dibutyl tindilaurate 4.1 Triphenyl phosphate 20.3 ¹T-1890 is the isocyanurate ofisophorone diisocyanate commercially available from Degussa. ²IONOL is2,6-Di-t-Butyl Cresol commercially available from Cognis.

Charge 1 was heated in the reactor to a temperature of 70° C. under anitrogen blanket. Upon reaching 70° C., Charge B was added over a periodof 45 minutes or at a rate to maintain the reaction temperature at nogreater than 80° C.

CHARGE B Component Weight (g) Sartomer SR-9003³ 929.6 Hydroxy ethylacrylate 929.6 ³Sartomer SR-9003 is a propoxylated neopentyl glycoldiacrylate monomer and is commercially available from Sartomer Company,Inc., Exton, PA.

Upon completion of the addition of Charge B, the reaction temperaturewas maintained at 80° C. for one hour. After the one-hour hold, Charge Cwas added.

CHARGE C Component Weight (g) 1,6-Hexanediol 236.92

With the addition of Charge C, the reaction was held until the NCO peakwas no longer visible in an IR spectra of the reaction material. Aftercompletion of the reaction, Charge D was added.

CHARGE D Component Weight (g) Sartomer SR-9003 808.4 Butyl acetate 811.8

The urethane acrylate had a resin solids content of 61.5% (measured at 1hour/110° C.) and a Gardner viscosity of W-Z2. The free hydroxylethylacrylate was <0.1%. The polyacrylate described above was used in thepreparation of the following coating compositions and is referred to asAcrylate 1.

The following examples illustrate coating compositions according to thepresent invention. Radiation-curable primer compositions were preparedby dispersing the pigments in the Acrylate 1 binder using a high-speedpneumatic motor equipped with a cowles stirring blade. Photoinitiator,solvent, and additives were then added to the dispersed pigment/acrylateblend as shown in Table 1.

TABLE 1* Raw Material Example 1 Example 2 Example 3 Example 4 Acrylate 1104.7 104.7 104.7 104.7 Propoxylated NPGDA¹ 8.4 8.4 8.4 8.4 Iron oxide².3 .3 .3 .3 Talc³ 26.1 26.1 26.1 26.1 Barium Sulfate⁴ 7.6 7.6 7.6 7.6Calcium carbonate⁵ 22.9 22.9 22.9 22.9 Titanium dioxide⁶ 2.6 2.6 2.6 2.6Phosphate ester acrylate⁷ 5.0 5.0 5.0 5.0 Tannic acid solution⁸ 6.7 6.7CPO resin solution⁹ 30.0 30.0 Photoinitiator¹⁰ 3.0 3.0 3.0 3.0 Acetone70.0 70.0 40.0 40.0 Total 250.6 257.3 250.6 257.3 *All weights in grams.¹Propoxylated neopentyl glycol diacrylate supplied as SR9003 fromSartomer Corp., Exton, PA. ²Commercially available as BAYFERROX Black318M from Bayer Corp. Pittsburgh PA. ³Commercially available asMICROTALC MP 15-38 from Barrets Minerals. ⁴Commercially available as2065 Barium Sulfate from Barrets Minerals. ⁵Commercially available asOMYACARB 3 from OMYA Inc. ⁶Commercially available as R960-38 Titaniumdioxide from DuPont Inc. ⁷Phosphoric acid ester acrylate commerciallyavailable as CD9052 from Sartomer Corp., Exton, PA. ⁸Prepared bydissolving 15 grams of Tannic acid in 85 grams of acetone. ⁹Preparedaccording to Example A of U.S. Pat. Publication No. 2006/0013958.¹⁰Commercially available as DAROCUR 4265 from Ciba Giegy Corp.

The compositions of Examples 1-4 were spray applied to a variety ofsubstrates and cured under an H&S Autoshot 400 watt UV lamp set at adistance of 10 inches for a total of two minutes. The cured primer wasthen topcoated with D9700 black basecoat, available from PPG Industriesand subsequently clearcoated with D893 urethane clearcoat also availablefrom PPG Industries. The test panels with the radiation cured primer,basecoat and clearcoat were then allowed to cure at ambient conditionsovernight before testing for adhesion according to ASTM D 3359. Theresults of the adhesion testing are shown in Table 2 below and arepresented as % of the complete coating system adhering to thesubstrates.

TABLE 2 Example Cold Rolled Steel Electrogalvanized Steel TPO-Plastic 10 0 0 2 100 97 0 3 0 0 100 4 100 100 100

Examples 1, 2 and 3 are comparative compositions. Example 4 is inaccordance with the present invention. As can be seen from the testresults set forth in Table 2 above, the coating composition according tothe present invention provides the best adherence over the variety ofsubstrates.

Examples 5-8

These UV-curable primer compositions may also be augmented by theaddition of polythiol functional oligomers and polymers. The addition ofthese materials increases cure response at the coatings surface and insome instances improves adhesion to various substrates.

The following examples were prepared by dispersing pigments in theurethane acrylate binder using a high speed pneumatic motor equippedwith a cowles stirring blade. Photoinitiator, solvent, and additiveswere then added to the dispersed pigment/urethane acrylate blend asshown in Table 3 (all weights are in grams). The thiol functionaloligomer was added immediately before application of the coating.

TABLE 3 Raw Material Example 5 Example 6 Example 7 Example 8 Urethaneacrylate¹ 104.7 104.7 104.7 104.7 Propoxylated NPGDA² 8.4 8.4 8.4 8.4Iron oxide³ .3 .3 .3 .3 Talc⁴ 26.1 26.1 26.1 26.1 Barium Sulfate⁵ 7.67.6 7.6 7.6 Calcium carbonate⁶ 22.9 22.9 22.9 22.9 Titanium dioxide⁷ 2.62.6 2.6 2.6 Phosphate ester acrylate⁸ 5.0 5.0 5.0 5.0 Tannic acidsolution⁹ 6.7 6.7 CPO resin solution¹⁰ 30.0 30.0 Photoinitiator¹¹ 3.03.0 3.0 3.0 Acetone 70.0 70.0 40.0 40.0 Pentaerythritol tetrakis 10 1010 10 mercaptopropionate Total 260.6 267.3 260.6 267.3 ¹Proprietaryurethane acrylate solution produced by PPG Industries Inc., PittsburghPA. ²Propoxylated neopentyl glycol diacrylate supplied as SR9003 fromSartomer Corp., Exton, PA. ³Supplied as Bayferrox Black 318M from BayerCorp., Pittsburgh PA. ⁴Supplied as Microtalc MP 15-38 from BarretsMinerals. ⁵Supplied as 2065 Barium Sulfate from Barrets Minerals.⁶Supplied as Omyacarb 3 from OMYA Inc. ⁷Supplied as R960-38 Titaniumdioxide from DuPont Inc. ⁸Phosphoric acid ester as CD9052 from SartomerCorp., Exton, PA. ⁹Prepared by dissolving 15 grams of Tannic acid in 85grams of acetone. ¹⁰Prepared according to Example A of U.S. Pat.Publication No. 2006/0013958. ¹¹Supplied as Darocur 4265 from Ciba GeigyCorp.

The UV curable primer compositions were spray applied to a variety ofsubstrates and cured under an H&S Autoshot 400 watt UV lamp set at adistance of 10 inches for a total of two minutes. The cured primer wasthen topcoated with D9700 black basecoat, available from PPG Industries,Inc. and clearcoated with D893 urethane clearcoat also available fromPPG Industries, Inc. The test panels with UV cured primer, basecoat andclearcoat were then allowed to cure at ambient conditions overnightbefore testing for adhesion according to ASTM D3359. The results of theadhesion testing are shown in Table 4 and are presented as % of thecomplete coating system adhering to the substrates.

TABLE 4 Electrogalvanized Example Cold Rolled Steel Steel TPO-Plastic 550 50 0 6 100 100 0 7 0 0 100 8 100 100 100

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

1. A radiation-curable coating composition comprising: 50 to 80 percentby weight of a radiation-curable compound, 1 to 5 percent by weight of afree acid, wherein the free acid is selected from tannic acid,phosphoric acid, gallic acid and/or citric acid; 1 to 10 percent byweight of a halogenated polyolefin; and 1 to 3 percent by weight of aphotoinitiator; wherein the percentages by weight are based on theweight of total resin solids in the composition.
 2. The composition ofclaim 1, wherein the radiation-curable compound comprises a urethanepolyacrylate.
 3. The composition of claim 1, wherein the compositionfurther comprises 5 to 25 percent by weight of a polythiol, wherein thepercentage by weight of the polythiol is based on the total weight ofthe radiation curable compound.
 4. The composition of claim 1 in whichthe free acid is tannic acid.
 5. A method of applying a coatingcomposition to a substrate, which comprises both metal and plastic, themethod comprising: (a) applying the radiation-curable composition ofclaim 1 to the substrate, and (b) curing the composition by ultravioletradiation.
 6. The method of claim 5 wherein the radiation-curablecomposition is applied to a substrate selected from metal, a plasticselected from thermoplastic polyolefin, thermosetting polyurethane,thermoplastic polyurethane and EPDM.
 7. The method of claim 5 furthercomprising applying a protective or decorative coating over the curedcomposition of step (b)
 8. A radiation-curable coating compositioncomprising: (a) 50 to 80 percent by weight of a radiation-curablecompound comprising a urethane polyacrylate, (b) 1 to 5 percent byweight of tannic acid, wherein the free acid is selected from tannicacid, phosphoric acid, gallic acid and/or citric acid; (c) 1 to 10percent by weight of a chlorinated polyolefin; (d) 1 to 3 percent byweight of a photoinitiator; and (e) 5 to 25 percent by weight of apolythiol; wherein the percentages by weight of (a), (b), (c) and (d)are based on the weight of total resin solids in the composition andwherein the percentage by weight of (e) is based on the total weight ofthe radiation curable compound (a).
 9. The composition of claim 8wherein the radiation-curable compound (a) comprises a urethanepolyacrylate.
 10. The composition of claim 1 in which the free acid istannic acid.
 11. A method of applying a coating composition to asubstrate, which comprises both metal and plastic, the methodcomprising: (A) applying the radiation-curable composition of claim 8 tothe substrate, and (B) curing the composition by ultraviolet radiation.12. The method of claim 11 wherein the radiation-curable composition isapplied to a substrate selected from metal, a plastic selected fromthermoplastic polyolefin, thermosetting polyurethane, thermoplasticpolyurethane and EPDM.
 13. The method of claim 11 further comprisingapplying a protective or decorative coating over the cured compositionof step (B).